A sagittal saw is a powered surgical tool often used in an orthopedic surgical procedure. A sagittal saw includes a body that houses a motor and the complementary control circuit that regulates the actuation of the motor. Extending forward, distally, from the body, is a planar saw blade. The most forward end of the saw blade is formed with teeth for cutting hard tissue, the bone, against which the blade is applied. A drive mechanism internal to the housing transfers the power developed by the motor to the blade. The drive mechanism of a conventional sagittal saw converts the rotary motion produced by the output shaft of the motor to the blade so that the distal end of the blade moves back-and-forth along an arc. This arc is in the plane in which the blade is aligned. Consequently, when a sagittal saw is actuated, the blade teeth move in a back-and-forth pattern against the tissue to which the teeth are applied. As a consequence of this motion and the forward pressure applied by the surgeon holding the saw, the teeth cut and separate the hard tissue or bone.
Conventional sagittal saws work reasonably well for the purposes for which they are intended. There is, however, a disadvantage associated with the conventional sagittal saw. This disadvantage is understood to by reference to FIGS. 1A and 1B. Initially it should be understood that as the distal end of a blade 40 sweeps against the bone to be cut, the blade teeth, as intended, plow into the this face of uncut bone. This plowing action scrapes the uncut bone away from the bone face. This scraped bone forms a mass of bone remnants, a collection of bone dust and bone chips. As mentioned above, a conventional sagittal saw causes the distal end of the attached blade to move in a back and forth pattern along an arc. In FIG. 1A, blade head 40 is shown sweeping to the right as represented by curved arrow 42. As a consequence the right side of the teeth, for example, tooth 44 is the side of the tooth that that plows into the bone and creates bone remnants 45. These bone chips accumulate in the space between the left side of tooth 44 and the right side of tooth 46. FIG. 1B, represents the return phase of the complete cycle of the displacement of the blade head 40. Blade head 40 sweeps to the left as represented by curved arrow 48. In this phase of the displacement of the distal end of the blade it is the left sides of the teeth that plow into the bone. As a consequence of this plowing action tooth 46 generates additional bone remnants 45 that fill the space between teeth 44 and 46.
It should therefore be appreciated that, when cutting bone, a large volume of bone remnants can rapidly accumulate between the blade teeth. During the cutting process, the blade is sandwiched top to bottom between two sections of uncut bone. Consequently the trapped bone chips are not simply, upon filling the spaces between the teeth, discharged upwardly or downwardly out of the kerf being cut in the bone. Further, it should be understood that often the arc across which any individual tooth sweeps typically has a length of 1.3 cm or less and more often 0.8 cm or less. The blade itself may have a width across that is 3 cm or less and often 2.5 cm or less. Micro sagittal blades have a width across the blade of 1.0 cm or less. Often these blades are positioned in bone so as to form kerfs that, until the bone is completely cut across are bordered on one if not both sides by uncut bone. This limits the ability of the accumulated bone chips from being discharged outwardly from the sides of the kerf being cut.
Thus, it should be appreciated that when cutting bone, especially large bones such as femur or tibia, in a relatively short amount of time, a significant volume of bone remnants can accumulate around the teeth of a surgical sagittal saw blade. These bone remnants impede the ability of the blade teeth to press into and cut away the remaining bone.
The Applicants' Assignee's U.S. Pat. No. 3,978,862 suggests one potential means of reducing the build up of bone chips in the kerf formed by a sagittal saw. This document discloses a saw capable of simultaneously pivoting a blade back and forth and moving the blade longitudinally within the blade mount. The saw of this invention is designed so that there is a 1:1 ratio in the right-to-left and back to right pivoting cycle of the blade and the front-to-right and back to front longitudinal displacement. In a single cycle, the blade head travels in an elliptical path. When this type of saw is actuated, in separate phases of the pivoting cycle, the attached blade moves both forward and away from the face of the bone against which the blade teeth are pressed.
Consequently, when a blade is actuated using this type of saw, the blade teeth travel in one direction around what can be described as a loop. In each cycle in which the blade is actuated, the blade, when it is most distal position is moved in one direction, to the right or to the left, of the extension of the longitudinal axis of the saw. As a result, when the blade is pressed against the surface of the bone the blade is intended to cut, the blade pulls in the direction, right or left, in which the blade is cycled. A surgeon using this blade must therefore apply a counterforce to counteract this biasing pull.